1. Field of the Invention
The present invention relates to a fuel cell. Particularly, the present invention relates to a fuel cell mounted on a vehicle or, more particularly, a cooling apparatus capable of warming up the fuel cell.
2. Description of the Related Art
In recent years, a fuel cell has attracted interest from the standpoint of its eco-friendliness, high efficiency and the like, and is under development as an energy source for vehicles. In a vehicle, when the fuel cell is used as its drive source, it is necessary to quickly warm up the fuel cell itself up to predetermined proper operating temperatures when starting a vehicle from a stopped state.
As a warming-up system of a fuel cell for a vehicle, a system for warming cooling water of the fuel cell by the use of a heater (for example, see Patent document 1) has been proposed in the prior art. This warming-up system of a fuel cell is an excellent system with high efficiency during the normal operation. However, in this case because the fuel cell is operated at temperatures of below 80° C. in order to secure the durability of membrane electrode assembly of the fuel cell, the difference in temperature from the temperature of the atmosphere, which is required to be large for dissipating heat to the atmosphere during the normal operation, cannot be so large and, at the same time, because the quantity of heat dissipated from a fuel cell is extremely large, two radiators are necessary currently, and it is undesirable that the two radiators occupy a large space in the vehicle. On the other hand, when starting the fuel cell which is quite cold after the stopped state, a considerable amount of energy is required for heating the fuel cell up to the normal operating temperature. Therefore, it is difficult to start the fuel cell in a short time, resulting in a degradation in efficiency.
There has been also proposed another warming-up system for a fuel cell (for example, see Patent document 2).
[Patent document 1]
Japanese Unexamined Patent Publication (Kokai) No. 7-94202
[Patent document 2]
Japanese Unexamined Patent Publication (Kokai) No. 2000-195533